This disclosure relates to thermoplastic compositions, in particular laser-weldable thermoplastic compositions, methods of manufacture, and articles thereof.
Thermoplastic compositions are used in the manufacture of a wide variety of products, including laser-welded products. Near-infrared (NIR) laser-welding of two polymer articles by transmission welding requires one of the polymer articles to be at least partially transparent to laser light, and the other to absorb a significant amount of the laser light. An additional key requirement is that there is good physical contact between the parts during a welding process; a smooth surface is beneficial in this respect. The laser passes through the first laser transparent layer and is absorbed by the second polymer layer, generating heat in the exposed area. External pressure is applied to ensure uninterrupted contact and heat conduction between the parts resulting in the melting of both the absorbing and the transmitting polymers, thus generating a weld at the interface.
The level of NIR transmission in the upper part should allow sufficient laser density at the interface to facilitate effective welding. Otherwise, the joining of the two materials by laser transmission welding is either impossible or restricted to slow scan speeds, which is not very attractive as it lengthens the part assembly cycle time. Crystalline, or partially crystalline materials, such as PBT, are materials that can easily disperse the incoming radiation. Consequently, the extent of the laser energy at the joining interface is dramatically diminished and the adhesion between the two layers is reduced. Scattering effects are greatly enhanced when fillers such as glass fibers are present especially when the upper layer thickness is greater than 1 mm. Therefore, the laser-welding of crystalline material and particularly glass filled versions, is restricted if not impossible in a lot of cases.